This invention relates to a radio frequency power coupling network and more particularly to such a network using a parallel plate transmission line.
A parallel plate transmission line used as part of a lens feed for an antenna array system is described in applicants' U.S. Pat. No. 3,827,055. The system described in the patent is an efficient way of beam steering through 360.degree. in fine increments or continuously. The parallel plate transmission line in the system of the above cited patent has a central set of coupling members for propagating in the transmit mode directional signals inside the parallel plate transmission line and a second set of coupling members located in a ring-like pattern about the first set of coupling members responsive in the transmit mode to the signals in the line. The outer coupling members of the second set are coupled via transmission lines to radiating antenna elements. The energy distribution provided by the inner or central set of coupling members controls the energy distribution to the second set of coupling members. If a load mismatch at any one of the radiating antenna elements occurs, reflections from the one mismatched radiating antenna element may cause the connected one of the second set of coupling members to radiate power in the parallel plate transmission line, causing an unwanted change in the power distribution within the parallel plate transmission line. In particular, this undesirable power distribution results from radiation by one of the second set of coupling members being picked up by adjacent coupling members of the second set of coupling members.
A problem in state-of-the-art radio frequency power dividers has been the provision for equal dividing of the power from a given source to any selected number of loads with a high degree of isolation between the loads and with a low insertion loss. Power combiners are also difficult to design with respect to isolation between sources, insertion loss, and the freedom to select the number of sources to be combined. It is desirable that power combiner and power divider networks operate at relatively high power levels. Conventional power combiner and power divider networks using conventional hybrids such as magic tee and short-slot hybrids become increasingly lossy and inefficient as the number of sources or loads increases. For example, where the power from twenty sources are combined, adding an extra source or two more or even doubling the number of sources may produce only a negligible increase in power. Likewise, power division by using a plurality of hybrids can be very lossy.